Charged particle beam systems such as electron beam inspection (EBI) systems are increasingly applied in advanced integrated circuit chip manufacturing. The system has high resolution that can be used to detect tiny physical defects that beyond the capability of optical defect inspection systems. Another advantage of EBI is that it can detect voltage contrast (VC) defects of electrical circuitry such as open circuit, short circuit or leakage underneath the wafer surface because of surface charge induced gray level (GL) variation.
In dynamic random access memory (DRAM) manufacturing, piping defects can be formed when there are voids or keyholes between word lines (WL) during inter-layer dielectric (ILD) deposition process. Conducting material such as polysilicon that fills the contact holes also fills the voids or keyholes between the neighboring contact plugs in the ILD, which causes electrical short between neighboring contact plugs This defect is very difficult to detect for non-annealed polysilicon plugs. Sometimes it requires a destructive polysilicon anneal process to enable EBI system to detect piping defect. Piping issue will become more challenging when DRAM feature size continues to shrink and the aspect ratio of the gap between WL becomes even larger.